Cell cultures are used for the production of a vast variety of products, and various methods and apparatus exist for the cultivation of cultures of bacterial and fungal cells, and cells from higher organisms, i.e. eucaryotic cells.
Eucaryotic cells are usable for the generation of a wide range of products, such as virus vaccines, such as, e.g., polio vaccines, cellular chemicals, such as, e.g. interferon and interleukin, immunobiologicals such as, e.g., monoclonal antibodies, and hormones, such as, e.g. insulin.
Eucaryotic cells can be made to grow in two basically different modes. Most eucaryotic cells can be induced to divide only if they are first allowed to attach to a surface or a solid substratum (anchorage dependent), while some can be induced to grow freely in a suspension (anchorage independent).
Nunc™ is producing stacked, communicating tray systems for cell cultivation, called Cell Factories. The Cell Factories can be used for small- or large-scale cultivation of both anchorage dependent and anchorage independent cells. They are suitable for the cultivation of anchorage dependent cells since they provide a large amount of growth surface in a small area with easy handling and low risk of contamination. Due to the simple construction and manageability, the communicating tray system offers an alternative to the substantially more complex and expensive bioreactor or to roller flasks.
However, during the cultivation and production phase the cells will consume oxygen, and produce carbon dioxide, leading to oxygen depletion and acidification of the growth medium. This, in turn, will limit growth and product synthesis. It is found that growth of the cells and cell-based production can be considerably improved if the cells are grown in a constant atmosphere of a defined composition.
Simply supplying gas to the stacked, communicating tray system by entering a defined mixture of gasses has the disadvantage that the individual culture trays are not uniformly provided with oxygen unless a very high flow is applied. Such a high flow may be very difficult to apply due to the fact that the gas must be delivered to the culture trays as sterile gas, i.e. the gas has to be passed through a sterile filter before entering the tray system. The sterile filters will normally not be able to withstand such a high flow, which in practice means that it is not possible to apply such a high flow. Another problem with a high flow rate of gas is that before the gas enters into the tray system the gas must be humidified by passing through a humidifier. Normally, there is an upper limit for the size of the flow through such a humidifier in order to ensure a proper humidification of the gas. If the gas is delivered to the tray system without having been humidified, the medium and/or the cells that are cultivated in the trays will become dehydrated and this, in turn, leads to an unfavourable culturing condition.
EP 0 592 936 describes a method of supplying a defined gas to a stacked, communicating tray system by using a microporous supply line made of a Teflon-type material with pore diameters of between 0.2 μm to 4.0 μm. The pores in the microporous supply line are an inherent feature of the material and the supply line does not have additional processed apertures. When filling or emptying the system with liquid, a bypass valve has to be used, since the microporous system does not have the capacity of rapid pressure equalization, due to the small pore size of the microporous supply line. If the pressure exceeds a certain critical value there it may be detrimental to the system and the system may crack etc.
In EP 0 592 936, it is only illustrated that gas is distributed to the first tray in a stacked, communication tray device. In other words, EP 0 592 936 does not disclose whether gas distribution through a microporous supply line gives a fast and uniform distribution of gas to all trays in a device.